Brake system for a motor vehicle having an actuator

Abstract

The invention relates to a braking system (100) for a motor vehicle having a reservoir (10) for brake fluid and wheel brakes (50, 54, 108, 112) having a pressure supply device (6) and a pressure modulator (30), the braking system (100) comprising a primary braking system (2) having a hydraulic pressure supply device (6) and a pressure modulator (30), to which two hydraulic wheel brakes (50, 54) are hydraulically connected, the braking system (100) comprising a dry secondary braking system (94) having two further wheel brakes (108, 112), to which a brake demand device (84) and an open and closed loop control unit (90) are connected, the open and closed loop control unit (90) being arranged to control the pressure supply device (6) on the basis of a transmitted brake demand.

Description

[Technical field]

[0001] The present invention relates to a braking system for a motor vehicle having a reservoir for brake fluid and wheel brakes with pressure application devices and pressure modulators. Known braking systems act hydraulically on two paths, diagonally or in a black and white split. In "brake by wire" systems, actuators realize this pressure actuation. The driver presses down on the simulator and a brake pressure request is generated and implemented by the actuators. The brake pressures on the front and rear axles are identical. [Background technology]

[0002] One drawback of the above-mentioned braking system is that the availability of the braking system is dependent, inter alia, on intact brake lines. To detect a fault in the braking system, complex functions for detecting air and leaks and for discriminating between failed systems are required. Successful fault detection results in fault-induced degradation of braking performance. No redundancy is provided to compensate for a failed system.

[0003] Hydraulic systems also have the drawback that the installation and filling of the hoses during production is relatively complicated. The aim is to find a solution that allows avoiding liquids and reducing process and / or work steps. With current systems, braking along with an ideal brake force balance as well as per-axle blending for regenerative braking cannot be achieved without loss of efficiency or comfort.

[0004] DE 10 2012217825 A1 discloses a combined braking system for a motor vehicle with a hydraulic braking system for the front axle, which is designed as a "brake-by-wire" braking system with electrically controllable pressure application devices with wheel brakes which can each be actuated by an electromechanical actuator.

[0005] DE 10 2017211953 A1 describes a braking system having a simulation unit with a simulator which can be operated with the aid of a brake pedal and an auxiliary module, the auxiliary module having a hydraulic unit with a pressure providing device for the active pressure accumulated in at least two of the wheel brakes.

[0006] DE 10 2017211955 A1 discloses a brake system with a further module, which comprises a hydraulic unit with a pressure supply device for the active pressure stored in at least two wheel brakes, where no hydraulic and / or mechanical operative connection exists between the brake pedal and the wheel brakes. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention is therefore based on the object of providing a braking system which is both reliable and flexibly installable. [Means for solving the problem]

[0008] According to the invention, this object is achieved in that a braking system comprises a primary braking system having a hydraulic pressure providing device and a pressure modulator to which two hydraulic wheel brakes are hydraulically connected, the braking system comprises a dry secondary braking system having two further wheel brakes, and a braking demand device and an open-loop and closed-loop control unit connected thereto are provided, the open-loop and closed-loop control unit being configured to operate the pressure providing device based on the transmitted braking demand.

[0009] Advantageous refinements are the subject matter of the dependent claims.

[0010] The present invention is based on the consideration that there exists a need for a reliable and stable "brake-by-wire" system that can be flexibly integrated into a given vehicle environment.

[0011] As recognized above, these requirements can be met by combining a hydraulic single-circuit braking system with an electric single-circuit braking system to provide a semi-dry braking system. Thus, the core of the invention is a service brake system (semi-dry braking system) for a motor vehicle having hydraulically actuable wheel brakes on a first axle and electromechanically actuable (e.g. dry) wheel brakes on the other axle, the pressure providing or actuating device being coupled by wire to the brake pedal or brake demand device, with the result that there is no hydraulic and / or mechanical intervention of the driver on the wheel brakes.

[0012] The braking system does not have simulator valves due to the "by wire" connection. The axles can be braked independently of each other. There is no need for two independent open and closed loop control units, nor is there a need for a separate power supply.

[0013] The "by wire" system acts hydraulically only on the front axle. The subsystem preferably comprises a separate brake actuation means (pedal unit) and a hydraulic block with an ECU and an actuator. The actuator is electrically connected to the pedal unit. The "by wire" system acts as a primary brake system and can be used as a master / host to actuate a secondary brake system. The overall system is combined with an electric brake in case of the rear axle. This means that the overall system is designed as a dual and redundant system.

[0014] The pressure applying device preferably has a single hydraulic pressure chamber, which is or can be hydraulically connected to the pressure modulator, so that the brake system has a hydraulic brake system or has a hydraulic single system configuration.

[0015] Advantageously, the brake demand device is designed as a driver brake demand detection device, which improves the brake system as a "brake by wire" brake system, since the driver has no hydraulic or mechanical intervention on the wheel brakes.

[0016] In a preferred embodiment, the brake system comprises a pedal unit, in which in particular a driver's brake request detection device is integrated. The pedal unit preferably generates the driver's request and transmits it to the brake system. For this purpose, the pedal unit comprises a separate logic circuit. This solution generates, as a result of the actuation, an item of information based on a signal, which is evaluated by the brake system / brake control unit and converted into the driver's brake request, i.e. into an individual deceleration request. This results in the implementation of a brake torque.

[0017] The pedal unit preferably comprises a pedal, in particular a dry pedal, and a pedal sensor which is designed to have redundancy.

[0018] In a preferred alternative embodiment, or in combination, the brake request device is configured as an autonomous driver or at least one autonomous driving function, which generates the deceleration request. The term "autonomous driver" preferably includes here functions that can generate the brake request autonomously without driver action. This means that a wide variety of comfort and assistance functions must be understood: hill start assistance, autobrake function with distance control, emergency braking, and autopilot systems.

[0019] The open and closed loop control units advantageously operate both the primary and secondary braking systems.

[0020] The primary and secondary braking systems can be configured with dedicated ECU open and closed loop control units, respectively, with the primary braking system having the lead. If the primary braking system is the host, the secondary braking system can be designed as a "hardware only" solution, where the primary braking system thus provides the actuation. As a result, any functionality and software content of the secondary braking system is located within the open and closed loop control units of the primary braking system.

[0021] The unit can be accommodated in the engine compartment, with the result that shorter lines are used for the front axle, which can save the costs induced when hydraulic calipers are fitted to the rear axle. For the purpose of axle load distribution, the front axle must have a stronger design. The response behavior of the hydraulic brakes can be adjusted relatively well according to the prior art.

[0022] The two hydraulic wheel brakes are preferably designed as front wheel brakes, the rear wheel brake is preferably designed as an electromechanical wheel brake (EMB).

[0023] The pressure modulator preferably has an inlet and an outlet valve for each connected wheel brake, the inlet and outlet valves being particularly preferably designed to be electrically actuable.

[0024] The pressure switching valve is preferably switched between the pressure supply device and the pressure modulator or the inlet valve. With the aid of this pressure switching valve, the pressure supply device or the actuator can be disconnected or connected to the pressure modulator as required. The pressure switching valve is particularly preferably designed to be electrically operable.

[0025] In addition to the pressure switching valve and the inlet and outlet valves, the primary brake system preferably does not have any further electrically actuable valves for each connected wheel brake. The primary brake system particularly preferably has exclusively the pressure switching valve, the two inlet valves and the two outlet valves as electrically actuable valves. This provides a particularly cost-effective brake system.

[0026] A hydraulic connection line connecting the port of the inlet valve opposite the pressure providing device to the reservoir and providing pressure equalization of the wheel brakes connected via the inlet valve to the reservoir in the non-energized state of the brake system is preferably not provided in the primary brake system.

[0027] In a preferred embodiment, the individual inlet valves and the individual outlet valves are designed as normally open valves and the pressure switching valve is designed as a normally closed valve. In this case, pressure equalization (e.g. of connected wheel brakes) to the reservoir (especially when the brake system is not energized) can be carried out via the outlet valve. If residual pressure is present in the brake system of the wheel brakes, this can be passively dissipated by the normally open outlet valve in the direction of the equalization tank / reservoir. The vehicle cannot therefore be immobilized by braking with this part of the brake system unintentionally. A linear actuator with an equalization opening or sniffer bore is not required to achieve pressure equalization to and from the container.

[0028] In a preferred alternative embodiment, the individual inlet valves are designed as normally open valves, the individual outlet valves are designed as normally closed valves, the pressure switching valves are designed as normally open valves, and the pressure providing device is designed in such a way that a hydraulic connection to the reservoir is formed in the idle state. Here, a hydraulic connection exists between the pressure chamber of the pressure providing device and the reservoir. In this case, pressure equalization (e.g. of the connected wheel brakes) can occur directly via the actuator in the non-energized case (non-energized state of the brake system). The wheel valves can be used in a standard configuration, with the result that a relatively small number of software adaptations have to be made for the function. The total current consumption is reduced.

[0029] In a preferred embodiment of the brake system, at least two wheel brakes have an integrated parking brake (IPB). In particular, the hydraulic front wheel brakes preferably have combined calipers, which in addition to the hydraulic service brake also each have an integrated parking brake. In an alternative embodiment, the dry rear wheel brake has an IBP or all four wheel brakes have an IBP. One of the two subsystems of the brake system (primary or secondary brake system) has to realize or guarantee a safe stop, which is advantageously performed by an electromechanical brake (EMB) on the rear axle. If the EMP cannot perform this function and / or redundancy is desired, an IPB combined caliper on the front axle is an advantageous solution. The IPB on the front axle is firstly able to realize a safe stop of the vehicle and secondly, in case of a hydraulic failure or fault, the IPB can also partially participate in the braking at the axle (IPB dynamic application).

[0030] Preferably, the open-loop and closed-loop control units are configured in such a way that the individual IBPs are activated at a fallback level to accumulate braking torque, in particular the IPBs act on a failed brake circuit when activated and assist the driver when braking hydraulically without boosting.

[0031] The advantages of the invention lie in particular in the fact that monitoring and testing routines can be simplified. The reduced complexity of the brake system allows a reduction in costs. The hydraulic subsystem can be combined with various electric brake systems. A master cylinder is not required, since the brake request is transmitted electronically by the pedal unit.

[0032] The actuator can have a smaller design than known brake systems, since it supplies only one brake line. Axle-by-axle blending is possible in the case of vehicles with regenerative capabilities. Braking along an optimal brake force distribution is possible. There are also advantages in terms of acoustics and space utilization, since the actuator does not have to be constructed on the bulkhead. This also results in less noise and favorable NVH (noise, vibration, harshness) behavior. Another advantage is improved crash performance, since the brake system cannot penetrate into the driver's footwell. The bulkhead does not have to take into account the accommodation of a heavy brake system in its design.

[0033] The braking system described can include an electric brake system on the rear axle with electric calipers, electric drum brakes, wheel hub motors, and a regenerative electric motor on the rear axle as a secondary brake system.

[0034] Due to its redundant design, the brake system offers improved safety because the front and rear axles can operate separately in case of failure of the other subsystem. Unlike one-box designs, the brake system is a distributed brake system. Defined interfaces can be used to allow components to be exchanged in a cross-sectional manner. When driving, braking along an optimal brake force distribution provides stability benefits up to its limits.

[0035] In the following section, an exemplary embodiment of the invention will be described in more detail with reference to the accompanying drawings, which are schematic diagrams, in which: [Brief description of the drawings]

[0036] [Figure 1]1 illustrates the primary brake system in a first preferred embodiment in a passive state. [Diagram 2] 2 illustrates the primary brake system of FIG. 1 in an active state. [Diagram 3] 1 illustrates a brake system in a preferred embodiment. [Figure 4] 3 shows a brake system in a further preferred embodiment. [Diagram 5] 3 shows a primary braking system in a further preferred embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] In all figures, identical parts are provided with the same designations.

[0038] 1 shows a primary braking system 2 designed as a one-line "brake-by-wire" system. It comprises a hydraulic block (not shown) with a pressure-providing device 6 designed as a linear actuator with an attached reservoir 10 for brake fluid or brake medium. The pressure-providing device 6 comprises a motor 14 with the help of which a pressure piston 18 moves into a hydraulic pressure chamber 22, and a motor position sensor 26, in particular designed as a rotation angle sensor, in particular designed with redundancy. The motor 14 is designed as an electric motor. To convert the rotational movement of the rotor of the motor 14 into a translational movement of the pressure piston 18, a rotational / translational gear mechanism, in particular designed as a ball screw drive (KGT), is provided.

[0039] The hydraulic block comprises a pressure modulator 30 with four wheel valves 34, 38, 42, 44, where the inlet valve 34 and the outlet valve 42 are hydraulically connected to a first front wheel brake 50, and the inlet valve 38 and the outlet valve 44 are hydraulically connected to a second front wheel brake 54. A check valve preventing the flow of braking medium from the pressure chamber 22 in the direction of the brake 50, 54 is connected in parallel in each case to the respective inlet valve 34, 38. A check valve preventing the flow of braking medium from the brake 50, 54 in the direction of the pressure chamber 22 is connected in parallel in each case to the respective outlet valve 42, 44. The outlet valves 42, 44 are connected to the reservoir 10 via compensation lines. The inlet valves 34, 38 and the outlet valves 42, 44 in this case have a normally open design.

[0040] A pressure switching valve 58, in this case of normally closed design and isolating the linear actuator from the system or the pressure modulator 30 if necessary, is arranged between the pressure chamber 22 and the pressure modulator 30. The operating pressure, i.e. the pressure prevailing in the pressure chamber 22, is measured with the aid of a pressure sensor 60, which is particularly designed for redundancy. The pressure chamber 22 is hydraulically connected to a reservoir 10 via a refill line 64, inside which a check valve 68 is connected. The reservoir 10 has two separate chambers 70, 72, which are separated from each other by an intermediate wall 76 up to a predefined height of the intermediate wall. The pressure chamber 22 is hydraulically connected to the two chambers 70, 72, with the consequence that in case of a leak inside one of the two chambers 70, 72 the brake fluid is still available. A brake fluid level sensor 80, which is particularly designed for redundancy, is provided for measuring the brake fluid level.

[0041] Advantageously, the primary brake system 2 has only five electrically actuable valves: one pressure switching valve 58 and four wheel valves 34, 38, 42, 44.

[0042] The primary brake system 2 further comprises a brake request device 84, which in this case is configured as a driver's brake request detection device 88 and is connected at the signal input to a brake pedal (not shown, in particular of the dry type). In an alternative embodiment, the brake request device 84 can be a brake request generation device of an autonomously driven vehicle, which realizes a deceleration request based on an autonomous driving function and transmits it to the brake control unit instead of the brake pedal. The brake request detection does not have to be generated by the driver via an actuator (pedal unit). Alternatively, the brake request generation can also be performed by a function that is not based on an actuator, i.e. is not directly / instantly triggered by the driver. The brake request detection between the driver and the function can overlap.

[0043] The braking system 2 further comprises an open and closed loop control unit 90 for operating the pressure providing device 6 and the valves 34, 38, 42, 44, 58. Figure 1 shows the primary braking system 2 in a passive state with no pressure position.

[0044] In the active state of the brake system 2 shown in Figure 2, the outlet valve is closed. When a pressure actuation demand reaches the linear actuator or pressure providing device 6, the open and closed loop control unit 90 opens the pressure switching valve 58 and the linear actuator builds up pressure in one or more of the wheel brakes 50, 54.

[0045] When the driver activates the brake pedal or brake unit, a deceleration request is generated in the driver's brake request detection device 88 and transmitted to a brake control unit or an open-loop or closed-loop control unit 90. The system shown in Figure 1 acting on the front axle is the primary brake system (PBS) 2. The brake system 100 according to the invention comprises a secondary brake system (SBS) 94, shown in Figure 3, which in this case acts on the rear axle.

[0046] The hydraulic primary system or primary brake system 2 can be combined with a brake system 94 acting electronically on the rear axle, with the result that both axles of the vehicle are braked. The primary brake system 2 now transmits a deceleration request to the secondary brake system 94, which now transmits its availability in advance to the primary brake system 2. Furthermore, the primary brake system 2 derives a pressure demand from the deceleration request, which it itself implements on the front axle. At the same time, a corresponding torque for deceleration is output on the rear axle.

[0047] This function is illustrated in FIG. 3, which also shows a pedal unit 104 and two rear wheel brakes 108, 112 of a secondary brake system 94, in this case with a dry design. Here, the two rear wheel brakes are designed in particular as electromechanical brakes. The driver's brake request detection device 88 is integrated in this case in the pedal unit 104. The connection of the driver's brake request detection device 88 to the secondary brake system 94 is a connection as a fallback level. In case the primary brake system 2 fails and is not able to send a request to the secondary brake system 94, the latter can also receive a request from the pedal unit via a bypass (fault condition with PBS2 failure). This also applies whenever a request does not come from the pedal unit 104 but from a function or an autonomous / virtual driver. The backup path 140, shown in FIGS. 3 and 4 as an arrow, symbolizes a path representing a fallback level / degradation or failure condition. The fallback level is explained below.

[0048] The ECU or open and closed loop control unit 90 of the primary brake system (PBS) 2 is used as a host for the whole system or brake system 100 in an alternative embodiment (shown in FIG. 4). The incoming deceleration request is calculated in the driver's brake request detection device 88 and distributed to corresponding braking torques for the front and rear axles. The open and closed loop control unit 90 of the primary brake system 2 acts as a host. Here, the secondary brake system 94 is no longer an independent unit as shown in FIG. 3. The secondary brake system 94 acts as an IPB (integrated HW). Thus, the secondary brake system 94 is integrated in the primary brake system 2. The pedal unit 104 sends the brake or deceleration request to the primary brake system 2. The primary brake system 2 receives the request as a host and calculates the torques for the front and rear axles. In the primary brake system 2, the individual target requirements are transferred to the linear actuator (LAC) and, in the case of the secondary brake system 94, to the associated actuator or EMB.

[0049] In case of failure of any part of the system, the vehicle can still be decelerated via the intact part of the system. In case of failure of the actuator of the PBS, the front axle can be braked hydraulically. Due to the actuator decoupling, direct intervention is not possible. In this case, the vehicle can only be decelerated via the rear axle. The following fault condition (fallback) levels or modes can be implemented: The first mode is a normal mode. The brake system 100 is in a no-fault state and operates as described above. In the second mode, the secondary brake system 94 is available while the primary brake system 2 has failed or malfunctioned. The secondary brake system 94 can convert the brake torque from the pedal unit 104 or from a function on the rear axle.

[0050] In the third mode, there is a defect or malfunction of the secondary brake system 94, with the result that only the primary brake system 2 can be used to brake. The brake system 100 can only implement deceleration requests on the front axle via the primary brake system 2.

[0051] In a fourth mode 4, the linear actuator of the primary brake system 2 is defective or malfunctioning. The open and closed loop control unit 90 is functioning such that the brake system 100 can operate in a cooperative mode. The primary brake system 2 can still send deceleration requests to the secondary brake system 2.

[0052] In the fifth mode, which is the emergency mode, the pedal unit 104 is defective or malfunctioning. The driver can no longer brake independently. A deceleration request is only possible via the secondary device (parking brake button or transmission P) or via the autonomous braking function.

[0053] The brake system 100 can have a combined brake caliper with an integrated parking brake (IPB) on the front axle brakes 50, 54. The IPB can be used here for a safe stopping of the vehicle. In this case, the IPB can also be used in case of failure of the actuator or the pressure providing device 6. If the actuator is not able to hydraulically build up pressure on the front axle, the IPB can be slowed down mechanically. This creates a fallback level, so to speak, in the primary brake system 2. This corresponds to "IPB dynamic application" according to VDA standard 305-100.

[0054] FIG. 5 shows a second preferred embodiment of the primary brake system 2 of the brake system 100, which allows passive equalization via the pressure providing device 6 and the linear actuator. For this purpose, the pressure switching valve 58 is designed as a normally open (NO) valve. In this case, the pressure providing device 6 is designed in such a way that in its idle state, i.e. in an unenergized state with the pressure piston 18 fully retracted, the volume can be returned to the reservoir 10. In the illustrated exemplary embodiment, this is realized by at least one equalization opening ("sniffer hole") 126, via which the pressure providing device 6 in the idle state is hydraulically connected to the reservoir by an equalization line 130. Alternatively, it is also possible to provide a hydraulic connection between the valves, via which equalization can occur in the idle state.

[0055] The inlet valves 34, 38 are designed as NO valves in this embodiment, and the outlet valves 42, 44 are designed as NC valves. Therefore, there is no need to activate the valves during hydraulic braking. The same valve setup can be used with other systems with normally open inlet valves and normally closed outlet valves. In addition, the pressure switching valve 58 or PFV (pressure supply valve) is also designed as a normally open valve. This results in a low current consumption and a relatively long service life, because the valves are switched and the energy supply is relatively small. In addition, the relatively small number of valve switching operations results in a relatively small noise. This pressure switching valve 58 does not need to be switched to build up pressure. [Explanation of symbols]

[0056] 2 Primary Brake System 6. Pressure supply device 10 Reservoir 14 Motor 18 Pressure Piston 22 Pressure Chamber 26 Motor Position Sensor 30 Pressure Modulator 34 Inlet valve 38 Inlet valve 42 Outlet valve 44 Outlet valve 50 Front Wheel Brake 54 Front wheel brake 58 Pressure Switching Valve 60 Pressure Sensor 64 Refill Line 68 Check valve 70 Chamber 72 Chamber 76 Intermediate Wall 80 Brake Fluid Level Sensor 84 Brake demand device 88 Driver's brake request detection device 90 Open and closed loop control units 94 Secondary Brake System 100 Brake System 104 Pedal unit 108 Rear wheel brake 112 Rear wheel brake 120 Check valve 126 Equalization aperture 130 Equalization Line 140 Backup Route

Claims

1. A brake system (100) for a motor vehicle having wheel brakes (50, 54, 108, 112) having a reservoir for brake fluid and a pressure providing device (6) and a pressure modulator (30), comprising: An optical illumination module for a display system comprising: The braking system (100) comprises a primary braking system (2) having two hydraulic wheel brakes (50, 54) hydraulically connected to the hydraulic pressure providing device (6) and the pressure modulator (30), the braking system (100) comprising a dry secondary braking system (94) having two further wheel brakes (108, 112), 2. A system comprising: a brake request device (84) and an open-loop and closed-loop control unit (90) connected thereto, the open-loop and closed-loop control unit (90) configured to operate the pressure providing device (6) based on a transmitted brake request.

2. 2. The braking system (100) of claim 1, wherein the brake demand device (84) is designed as a driver brake demand detection device (88).

3. 3. A braking system (100) according to claim 2, comprising a pedal unit (104), in particular the driver's brake request detection device (88) being integrated in the pedal unit (104).

4. The braking system (100) of claim 2, wherein the brake demand device (84) is designed as an autonomous driver.

5. The braking system (100) of any one of claims 1 to 4, wherein the open and closed loop control unit (90) operates both the primary braking system (2) and the secondary braking system (94).

6. Braking system (100) according to any one of claims 1 to 5, wherein the two hydraulic wheel brakes (50, 54) are designed as front wheel brakes.

7. The braking system (100) of any one of claims 1 to 6, wherein a pressure switching valve (58) is switched between the pressure providing device (6) and the pressure modulator (30).

8. 8. The braking system (100) of claim 7, wherein the pressure modulator (30) has an inlet valve (34, 38) and an outlet valve (42, 44) for each connected wheel brake (50, 54).

9. 9. The braking system (100) of claim 8, wherein in addition to the pressure switching valve (58) and the inlet and outlet valves, the primary brake system (2) does not have any further electrically operable valves for each connected wheel brake (34, 38, 42, 44).

10. 10. The braking system (100) of claim 8 or 9, wherein the individual inlet valves (34, 38) and the individual outlet valves (42, 44) are designed as normally open valves, and the pressure switching valve (58) is designed as a normally closed valve.

11. 10. A brake system (100) according to claim 8 or 9, wherein the individual inlet valves (34, 48) are designed as normally open valves, the individual outlet valves (42, 44) are designed as normally closed valves, the pressure switching valve (58) is designed as a normally open valve, and the pressure providing device (6) is designed in such a way that a hydraulic connection to the reservoir (10) is formed in the idle state.

12. The braking system (100) of any one of claims 1 to 11, wherein at least two wheel brakes (50, 54, 108, 112) have an integrated parking brake.

13. 13. The braking system (100) of claim 12, wherein the open and closed loop control unit (90) is configured to activate the individual integrated parking brakes, in particular at a fallback level.

Images